Why you should never use multi pattern mics

[kingkorg]

I've been thinking about sharing this for a while now as i've never read anything about this before. Please understand that there are exceptions, and if you like using your favorite LDC in figure of eight (or omni) there is nothing wrong with that, but you might want to understand what is really going on.

I almost never use multi pattern mics. There are several things happening at the same time, so i'll try to break them down.

The first issue is something I call ''electrical polar pattern fighting the mechanical one''. The other issue is the fact that sound is picked up by two membranes spaced apart by the thickness of the backplate. So you get phasing issues.

Electrical polar pattern fighting the mechanical one.

Let's take double sided/dual membrane K67(or k47, c12) capsule as example. Now imagine only one side is active, the other is not and for all intents and purposes doesn't exist in cardioid mode. You get frequency response like this:

We are interested in the green line which is 180 degree response. Most people think of cardioids as if they reject everything coming from the rear. This couldn't be further from the truth. 180 degree response is just 5 db bellow the 0 degree response at 5K where our ears are quite sensitive. This 180 degree response is created by the sound hitting the FRONT diaphragm coming through the mechanical delay network of the capsule's backplate, and not the REAR diaphragm which is in this mode disabled.

Now imagine we activate the rear diaphragm in such manner that we form figure of eight pattern. And we do get indeed, with an ideal capsule, F8 pattern with identical responses. The sound coming from each side of the capsule is now dominated by the sound coming from both physical diaphragms. We have achieved this by applying polarization voltage, and now both diaphragms are engaged. But what happened to that green 180 degree response we had in the previous image which was created by the sound coming through the rear diaphragm and the backplate and eventually hit the front diaphragm in opposite phase? Did it disappear? Well that's the thing people don't usually think about. It is still here, masked by the electrical signal created by the rear diaphragm. It is still just -5db at 5K, and it is mixed with the electrical signal. However it is PHASE SHIFTED by the distance between the diaphragms (approximately backplate thickness)!!! Of course this is true for the sound coming from both sides, there is no front or rear diaphragm per se, the capsule is symmetrical.

The issue of two diaphragms
This is basically explained above, but to simplify it even further, by using double sided capsule you actually have two microphones facing in opposite directions, however due to the capsule nature they are always somewhat phase shifted due to diaphragm separation. If you line up two mics as close as possible for any source in front of them, why would you do it any different in this case? Ideally you wouldn't, the same principle applies. Which brings me to the point. See how simple and elegant construction of a ribbon mic is. One ribbon, symmetrical construction, the sound coming from all around is hitting the diaphragm (the ribbon) at the same time, no delay of any sorts, no backplate in between, and no ''electrical'' signal messing with the ''mechanical''.

The same really goes for omni mode, or any pattern in between.

There is also one more issue with a lot of multi pattern mics. The electrical paths from the front and back diaphragm of the capsule to the impedance converter are rarely identical. Which can make all sorts of issues, mediocre both polar and frequency responses for example. In some, quite common topologies, one side of the capsule can stay charged even though the pattern is changed, which could mean you are using some random pattern between F8 and omni without realizing, yet thinking you are in cardioid.

If I want F8 response I simply use a ribbon mic. If I want omni, I just go for omni mic which utilizes one diaphragm. There are some different, yet exotic solutions, special capsule designs that try to avoid these issues. I personally use, if I have to, dual out mics such as Townsend Labs Sphere which allow me to virtually move diaphragms closer to each other by time aligning signals. The electronic path from both sides is also identical. But again, it will never give me phase coherent signal as ribbon or omni mics.

2023 update with measurement where two of the diaphragms are virtually aligned in omni to showcase the described issue:

Why you should never use multi pattern mics

 

[Purplenoise]

I've been thinking about sharing this for a while now as i've never read anything about this before. Please understand that there are exceptions, and if you like using your favorite LDC in figure of eight there is nothing wrong with that, but you might want to understand what is really going on.

I almost never use multi pattern mics. There are several things happening at the same time, so i'll try to break them down.

The first issue is something I call ''electrical polar pattern fighting the mechanical one''. The other issue is the fact that sound is picked up by two membranes spaced apart by the thickness of the backplate. So you get phasing issues.

Electrical polar pattern fighting the mechanical one.

Let's take double sided/dual membrane K67(or k47, c12) capsule as example. Now imagine only one side is active, the other is not and for all intents and purposes doesn't exist in cardioid mode. You get frequency response like this:

We are interested in the green line which is 180 degree response. Most people think of cardioids as if they reject everything coming from the rear. This couldn't be further from the truth. 180 degree response is just 5 db bellow the 0 degree response at 5K where our ears are quite sensitive. This 180 degree response is created by the sound hitting the FRONT diaphragm coming through the mechanical delay network of the capsule's backplate, and not the REAR diaphragm which is in this mode disabled.

Now imagine we activate the rear diaphragm in such manner that we form figure of eight pattern. And we do get indeed, with an ideal capsule, F8 pattern with identical responses. The sound coming from each side of the capsule is now dominated by the sound coming from both physical diaphragms. We have achieved this by applying polarization voltage, and now both diaphragms are engaged. But what happened with that green 180 degree response we had in the previous image which was created by the sound coming through the rear diaphragm and the backplate and eventually hit the front diaphragm in opposite phase? Did it disappear? Well that's the thing people don't usually think about. It is still here, masked by the electrical signal created by the rear diaphragm. It is still just -5db at 5K and it is mixed with the electrical signal however it is PHASE SHIFTED by the distance between the diaphragms (approximately backplate thickness)!!! Of course this is true for the sound coming from both sides, there is no front or rear diaphragm per se, the capsule is symmetrical.

The issue of two diaphragms
This is basically explained above, but to simplify it even further, by using double sided capsule you basically have two microphones facing in opposite directions, however due to the capsule nature they are always somewhat phase shifted due to diaphragm separation. If you line up two mics as close as possible for any source in front of them, why would you do it differently in this case? Ideally you wouldn't, the same principle applies. Which brings me to the point, see how simple and elegant construction of a ribbon mic is. One ribbon, symmetrical construction, the sound coming from all around is hitting the diaphragm(the ribbon) at the same time, no delay of any sorts, no backplate in between, and no ''electrical'' signal messing with the ''mechanical''.

The same really goes for omni mode, or any pattern in between.

There is also one more issue with a lot of multi pattern mics. The electrical paths from the front and back diaphragm of the capsule to the impedance converter are rarely identical. Which can make all sorts of issues, mediocre both polar and frequency responses. In some, quite common topologies, one side of the capsule can stay charged even though the pattern is changed, which could mean you are using some random pattern between F8 and omni without realizing, yet thinking you are in cardioid.

If I wand F8 response I just use a ribbon mic. If I want omni, I just go for omni mic which utilizes one diaphragm. There are some different yet exotic solutions, special capsule designs that try to bypass these issues. I personally use if I have to dual out mics such as Townsend Labs Sphere which allow me to virtually move diaphragms closer to each other by time aligning signals. The electronic path from both sides is also identical. But again, it will never give me phase coherent signal as ribbon or omni mics.

Great topic and post…should be a very interesting discussion.
My personal experience is I never felt comfortable using any other pattern other than cardioid in multi pattern mics. Somehow it sounds phasey, hollow and unnatural in most cases.
Pure Omni sdc’s sound much better and natural to me.
My most used mics are pure cardioid.

 

[soliloqueen]

just for raw comparison, this is a signal and the signal canceled with itself at a wavelength of 6mm over the entire audible band

it agrees with the measurements more or less perfectly. This is of course theoretical so real-world performance is even worse.

 

[living sounds]

Interesting! I also hardly ever like anything but cardiod mode with multipattern mics.

But Karen Carpenter was recorded with a U87 in omni mode with her standing very close to and singing against the soundproof window. Those recordings sound sublime...

 

[Icantthinkofaname]

I've been thinking about sharing this for a while now as i've never read anything about this before. Please understand that there are exceptions, and if you like using your favorite LDC in figure of eight there is nothing wrong with that, but you might want to understand what is really going on.

I almost never use multi pattern mics. There are several things happening at the same time, so i'll try to break them down.

The first issue is something I call ''electrical polar pattern fighting the mechanical one''. The other issue is the fact that sound is picked up by two membranes spaced apart by the thickness of the backplate. So you get phasing issues.

Electrical polar pattern fighting the mechanical one.

Let's take double sided/dual membrane K67(or k47, c12) capsule as example. Now imagine only one side is active, the other is not and for all intents and purposes doesn't exist in cardioid mode. You get frequency response like this:

We are interested in the green line which is 180 degree response. Most people think of cardioids as if they reject everything coming from the rear. This couldn't be further from the truth. 180 degree response is just 5 db bellow the 0 degree response at 5K where our ears are quite sensitive. This 180 degree response is created by the sound hitting the FRONT diaphragm coming through the mechanical delay network of the capsule's backplate, and not the REAR diaphragm which is in this mode disabled.

Now imagine we activate the rear diaphragm in such manner that we form figure of eight pattern. And we do get indeed, with an ideal capsule, F8 pattern with identical responses. The sound coming from each side of the capsule is now dominated by the sound coming from both physical diaphragms. We have achieved this by applying polarization voltage, and now both diaphragms are engaged. But what happened with that green 180 degree response we had in the previous image which was created by the sound coming through the rear diaphragm and the backplate and eventually hit the front diaphragm in opposite phase? Did it disappear? Well that's the thing people don't usually think about. It is still here, masked by the electrical signal created by the rear diaphragm. It is still just -5db at 5K and it is mixed with the electrical signal however it is PHASE SHIFTED by the distance between the diaphragms (approximately backplate thickness)!!! Of course this is true for the sound coming from both sides, there is no front or rear diaphragm per se, the capsule is symmetrical.

The issue of two diaphragms
This is basically explained above, but to simplify it even further, by using double sided capsule you basically have two microphones facing in opposite directions, however due to the capsule nature they are always somewhat phase shifted due to diaphragm separation. If you line up two mics as close as possible for any source in front of them, why would you do it any different in this case? Ideally you wouldn't, the same principle applies. Which brings me to the point. See how simple and elegant construction of a ribbon mic is. One ribbon, symmetrical construction, the sound coming from all around is hitting the diaphragm(the ribbon) at the same time, no delay of any sorts, no backplate in between, and no ''electrical'' signal messing with the ''mechanical''.

The same really goes for omni mode, or any pattern in between.

There is also one more issue with a lot of multi pattern mics. The electrical paths from the front and back diaphragm of the capsule to the impedance converter are rarely identical. Which can make all sorts of issues, mediocre both polar and frequency responses. In some, quite common topologies, one side of the capsule can stay charged even though the pattern is changed, which could mean you are using some random pattern between F8 and omni without realizing, yet thinking you are in cardioid.

If I want F8 response I simply use a ribbon mic. If I want omni, I just go for omni mic which utilizes one diaphragm. There are some different, yet exotic solutions, special capsule designs that try to avoid these issues. I personally use if I have to dual out mics such as Townsend Labs Sphere which allow me to virtually move diaphragms closer to each other by time aligning signals. The electronic path from both sides is also identical. But again, it will never give me phase coherent signal as ribbon or omni mics.

Now, if we want to use a figure 8 mic, but not use a ribbon mic, what are the options for small diaphragm capsules? I know Schoeps has a figure 8 one, and Sennheiser has the MKH30, and AKG has some figure 8 capsules. But what about either aftermarket ones, and do you know if the MK-012 figure 8 capsules (MK-012 figure-of-eight capsule) are mechanically figure 8, or 2 cardioids with adjusted phase like the figure 8 adapter makes?

I can't really think of a situation I need figure 8 in the first place (unless I want really heavy proximity effect which I can mimic with EQ), except maybe mid/side stereo, or miking two sources which I could just do with 2 cardioid mics (instead of using f8 for a duet or horizontally to capture vocals and guitar).

 

[emrr]

As an engineer making records and doing live broadcasts, in practice I find extremely few problems. There are plenty of reasons to use figure 8 over cardioid, and a U-67 in figure 8 sounds ‘just fine’. Any theoretical superiorities will be completely overwhelmed by aesthetic desires. I put up u67 in 8 along with mkh30 all the time. Or some ribbon. Or UMT70S in 8. Or use my modified TLM67 in wide cardioid. None is superior in any way other than what source dependent preferences are heard on any one type. There’s no more error than with any coincident stereo technique, and the way the stereo image is affected inevitably by imperfections in relative placement. Even the oktava MK-012 figure 8 adapter with its very wide capsule offset sounds good in MS with an LDC mid. The Pearl ELM-A is superb in all patterns, as is the MKH800 Twin; I use both. If I know I want omni it’s always a proper pressure transducer. I just did grand piano with close drums onstage in a big band using constructed virtual pattern pairs of omni’s and figure 8’s. No interaction problems at any blend ratio, just a choice of what’s best for isolation and piano sound in the mix. The Lauten LS-208 and LS-308 exploit an offset dual capsule approach to create 2nd order cardioids (at some unidentified frequency, ha!), and they have their place. I’ve used both onstage and in recordings. I get the theoretical points, I just don’t find them to present practical problems.

 

[soliloqueen]

one time i used a cardioid mic and an omni mic that were a foot apart to construct a mid-side stereo recording. there are no gods, only men.

 

[soapfoot]

In the real world, multi pattern mics can be useful and expedient, but multi-diaphragm omni and fig 8 are only approximations of pressure and velocity behavior (not the pure physics of a ribbon or pressure sensor) and it’s useful to understand that.

Even in practice, this can matter considerably. A good U47 sounds spectacular in cardioid, unremarkable in omni (for one of many examples).

From the other angle, “B” (“bidirectional”) is the only position I really use on an RCA 77… the acoustical labyrinth-derived “unidirectional” and “non-directional” (cardioid and omni) approximations are nowhere near that mic’s strengths.

There’s something to be said for letting a technology play to its natural strengths

 

[emrr]

From the other angle, “B” (“bidirectional”) is the only position I really use on an RCA 77… the acoustical labyrinth-derived “unidirectional” and “non-directional” (cardioid and omni) approximations are nowhere near that mic’s strengths.

I’ve noticed you’ve said that before. My D in L3 is really the ‘U87 of ribbons’ EQ, pretty useful, good on some guitar amps and vocals, unlike most other ribbons. It’s too bad there’s no historical survey of 77 pattern preferences, given the cultural imprint of it’s sound on old records. I’ve used omni there in a pinch for some shouty group vocals (coulda used anything) and 8 out front of drums recently, where it’s darker sound worked well. Would love to hear Les Watts modern take on the multi-pattern ribbon, but it’s not in budget. Samar keeps threatening to make one also.

 

[soapfoot]

Yeah, different individuals will have different impressions, and everything is “a sound” and is therefore useful sometimes.

On multi pattern condensers, I’d rather have the multiple patterns than to not have them.

At the barest of minima, the ability to put a U87 or 414 into omni for live room talkback is hugely convenient.

 

[living sounds]

For figure 8 the Coles 4038 is hard to beat IMO, especially combined with a good EQ to compensate for the FR.

 

[shabtek]

The ear/brain fills in blanks and glosses over what may show as anomalous on a measurement

 

[k brown]

The first post describes the main reason most of the major classical labels stopped using LDCs for anything, beyond the first few years of stereo. Decca, for example, began using M49s for opera voice spots, but very soon switched to SDCs for everything. Marc Aubort (Vox, Vanguard, and many others) never used LDCs for anything.

The other reason is the slower transient response of LDCs.

 

[emrr]

Then there's the Straus Paket approach of combining a pair of mics to create a different pattern, used until Neumann made an SDC with a wide cardioid pattern. Pattern control trumped potential problems, and the technique was surely capable of introducing errors greater than a multi-pattern LDC or SDC.

 

[Icantthinkofaname]

The first post describes the main reason most of the major classical labels stopped using LDCs for anything, beyond the first few years of stereo. Decca, for example, began using M49s for opera voice spots, but very soon switched to SDCs for everything. Marc Aubort (Vox, Vanguard, and many others) never used LDCs for anything.

The other reason is the slower transient response of LDCs.

Is the transient response difference due to capsules or the fact that many LDCs have transformers?

 

[emrr]

Is the transient response difference due to capsules or the fact that many LDCs have transformers?

Capsule mass. Same reason moving coil mics are even 'slower'.

 

[Icantthinkofaname]

Yeah, different individuals will have different impressions, and everything is “a sound” and is therefore useful sometimes.

On multi pattern condensers, I’d rather have the multiple patterns than to not have them.

At the barest of minima, the ability to put a U87 or 414 into omni for live room talkback is hugely convenient.

I agree as long as they sound good. Though I really prefer small diaphragm condensers but getting all the different pattern capsules for them can be pricey.

 

[Jen]

I've been thinking about sharing this for a while now as i've never read anything about this before. Please understand that there are exceptions, and if you like using your favorite LDC in figure of eight (or omni) there is nothing wrong with that, but you might want to understand what is really going on.

I almost never use multi pattern mics. There are several things happening at the same time, so i'll try to break them down.

The first issue is something I call ''electrical polar pattern fighting the mechanical one''. The other issue is the fact that sound is picked up by two membranes spaced apart by the thickness of the backplate. So you get phasing issues.

Electrical polar pattern fighting the mechanical one.

Let's take double sided/dual membrane K67(or k47, c12) capsule as example. Now imagine only one side is active, the other is not and for all intents and purposes doesn't exist in cardioid mode. You get frequency response like this:

We are interested in the green line which is 180 degree response. Most people think of cardioids as if they reject everything coming from the rear. This couldn't be further from the truth. 180 degree response is just 5 db bellow the 0 degree response at 5K where our ears are quite sensitive. This 180 degree response is created by the sound hitting the FRONT diaphragm coming through the mechanical delay network of the capsule's backplate, and not the REAR diaphragm which is in this mode disabled.

Now imagine we activate the rear diaphragm in such manner that we form figure of eight pattern. And we do get indeed, with an ideal capsule, F8 pattern with identical responses. The sound coming from each side of the capsule is now dominated by the sound coming from both physical diaphragms. We have achieved this by applying polarization voltage, and now both diaphragms are engaged. But what happened to that green 180 degree response we had in the previous image which was created by the sound coming through the rear diaphragm and the backplate and eventually hit the front diaphragm in opposite phase? Did it disappear? Well that's the thing people don't usually think about. It is still here, masked by the electrical signal created by the rear diaphragm. It is still just -5db at 5K, and it is mixed with the electrical signal. However it is PHASE SHIFTED by the distance between the diaphragms (approximately backplate thickness)!!! Of course this is true for the sound coming from both sides, there is no front or rear diaphragm per se, the capsule is symmetrical.

The issue of two diaphragms
This is basically explained above, but to simplify it even further, by using double sided capsule you actually have two microphones facing in opposite directions, however due to the capsule nature they are always somewhat phase shifted due to diaphragm separation. If you line up two mics as close as possible for any source in front of them, why would you do it any different in this case? Ideally you wouldn't, the same principle applies. Which brings me to the point. See how simple and elegant construction of a ribbon mic is. One ribbon, symmetrical construction, the sound coming from all around is hitting the diaphragm (the ribbon) at the same time, no delay of any sorts, no backplate in between, and no ''electrical'' signal messing with the ''mechanical''.

The same really goes for omni mode, or any pattern in between.

There is also one more issue with a lot of multi pattern mics. The electrical paths from the front and back diaphragm of the capsule to the impedance converter are rarely identical. Which can make all sorts of issues, mediocre both polar and frequency responses for example. In some, quite common topologies, one side of the capsule can stay charged even though the pattern is changed, which could mean you are using some random pattern between F8 and omni without realizing, yet thinking you are in cardioid.

If I want F8 response I simply use a ribbon mic. If I want omni, I just go for omni mic which utilizes one diaphragm. There are some different, yet exotic solutions, special capsule designs that try to avoid these issues. I personally use, if I have to, dual out mics such as Townsend Labs Sphere which allow me to virtually move diaphragms closer to each other by time aligning signals. The electronic path from both sides is also identical. But again, it will never give me phase

I've been thinking about sharing this for a while now as i've never read anything about this before. Please understand that there are exceptions, and if you like using your favorite LDC in figure of eight (or omni) there is nothing wrong with that, but you might want to understand what is really going on.

I almost never use multi pattern mics. There are several things happening at the same time, so i'll try to break them down.

The first issue is something I call ''electrical polar pattern fighting the mechanical one''. The other issue is the fact that sound is picked up by two membranes spaced apart by the thickness of the backplate. So you get phasing issues.

Electrical polar pattern fighting the mechanical one.

Let's take double sided/dual membrane K67(or k47, c12) capsule as example. Now imagine only one side is active, the other is not and for all intents and purposes doesn't exist in cardioid mode. You get frequency response like this:

We are interested in the green line which is 180 degree response. Most people think of cardioids as if they reject everything coming from the rear. This couldn't be further from the truth. 180 degree response is just 5 db bellow the 0 degree response at 5K where our ears are quite sensitive. This 180 degree response is created by the sound hitting the FRONT diaphragm coming through the mechanical delay network of the capsule's backplate, and not the REAR diaphragm which is in this mode disabled.

Now imagine we activate the rear diaphragm in such manner that we form figure of eight pattern. And we do get indeed, with an ideal capsule, F8 pattern with identical responses. The sound coming from each side of the capsule is now dominated by the sound coming from both physical diaphragms. We have achieved this by applying polarization voltage, and now both diaphragms are engaged. But what happened to that green 180 degree response we had in the previous image which was created by the sound coming through the rear diaphragm and the backplate and eventually hit the front diaphragm in opposite phase? Did it disappear? Well that's the thing people don't usually think about. It is still here, masked by the electrical signal created by the rear diaphragm. It is still just -5db at 5K, and it is mixed with the electrical signal. However it is PHASE SHIFTED by the distance between the diaphragms (approximately backplate thickness)!!! Of course this is true for the sound coming from both sides, there is no front or rear diaphragm per se, the capsule is symmetrical.

The issue of two diaphragms
This is basically explained above, but to simplify it even further, by using double sided capsule you actually have two microphones facing in opposite directions, however due to the capsule nature they are always somewhat phase shifted due to diaphragm separation. If you line up two mics as close as possible for any source in front of them, why would you do it any different in this case? Ideally you wouldn't, the same principle applies. Which brings me to the point. See how simple and elegant construction of a ribbon mic is. One ribbon, symmetrical construction, the sound coming from all around is hitting the diaphragm (the ribbon) at the same time, no delay of any sorts, no backplate in between, and no ''electrical'' signal messing with the ''mechanical''.

The same really goes for omni mode, or any pattern in between.

There is also one more issue with a lot of multi pattern mics. The electrical paths from the front and back diaphragm of the capsule to the impedance converter are rarely identical. Which can make all sorts of issues, mediocre both polar and frequency responses for example. In some, quite common topologies, one side of the capsule can stay charged even though the pattern is changed, which could mean you are using some random pattern between F8 and omni without realizing, yet thinking you are in cardioid.

If I want F8 response I simply use a ribbon mic. If I want omni, I just go for omni mic which utilizes one diaphragm. There are some different, yet exotic solutions, special capsule designs that try to avoid these issues. I personally use, if I have to, dual out mics such as Townsend Labs Sphere which allow me to virtually move diaphragms closer to each other by time aligning signals. The electronic path from both sides is also identical. But again, it will never give me phase coherent signal as ribbon or omni mics.

For Symphonic recording, I combine Wallaces 3 point 'Decca Tree' with M-S in the point position instead of a single mic. For M-S I mount a Sennheiser MKH-30 Fig8, capsule coincident just under a Josephson C617set omni. The rear flanks in the triangle are also Josephson C617set omni mics. A heavily modified 4 channel Millenia Media Systems HV-3D preamp includes 4 raw outputs, and an inboard M-S matrix with L and R mixer, giving a stereo out, direct to 2 track DSD. Mix is accomplished by the main input level controls, resulting in absolute minimum equipment in the signal path. I absolutely prefer the sound of dedicated pattern mics for purist sound in far-field recordings. For near field vocals, I use dedicated single pattern cardioids by Neumann and others, again non adjustable, not chosen for absolute linearity, but for their specific colorations. I have only 1 multi pattern mic, a 1940s era Western Electric 639a/b ribbon/dynamic, but I always use it in one single mode, never combined.

 

[k brown]

Sorry to be pedantic, but a tree of mics with MS at center is not a Decca Tree - it's just a mic tree.

 

[k brown]

one time i used a cardioid mic and an omni mic that were a foot apart to construct a mid-side stereo recording. there are no gods, only men.

One card and one omni for MS - how does that work, exactly?